Compounds containing the quinone (cyclohexadienedione) moiety are involved in a wide variety of biochemical processes including electron transport and oxidative phosphorylation (Morton). Many quinone compounds are naturally occurring, such as o-benzoquinone, fumigatin (3-hydroxy-2-methoxy-5-methyl-1,4-benzoquinone), daunorubicin, adriamycin, lapachol, and phthiocol (2-hydroxy-3-methyl-1,4-naphthoquinone). The K vitamins are all 1,4-naphthoquinone compounds or compounds that are oxidized to contain the 1,4-naphthoquinone moiety and are present in the blood as coagulation factors. Another naturally occurring 1,4-naphthoquinone compound is coenzyme Q, which occurs in many kinds of cells and is involved in electron transport.
A wide variety of quinone derivatives have been synthesized to date, and various structurally diverse quinone compounds have been reported to be biologically active. As an illustration, various quinone compounds have been reported to possess enzyme inhibitory (Hoffmann-Ostenhof), antibacterial (Ambrogi), antimalarial (Fieser), metabolite antagonist (Hoover), and antifungal (Webb, Entwistle) activities.
Various synthetic and naturally occurring quinone compounds have been reported to exhibit antitumor properties. One example of such compounds, early recognized to exhibit antitumor properties, is the mitomycins, a group of antitumor antibiotics produced by Streptomyces caespitosus (griseovinaceseus). Included in this class is mitomycin C, an antineoplastic agent and inhibitor of nucleic acid synthesis (Lin). The mitomycins are heterocyclic quinone compounds, and the early discovery of the biological activity of these compounds has led to the synthesis and investigation of large numbers of heterocyclic quinone derivatives.
As part of its ongoing efforts to obtain new antitumor drug candidates, since the late 1950s, the National Cancer Institute (NCI) has screened over 700,000 synthetic compounds (Griffin). As part of this effort, the NCI has screened approximately 1500 quinones falling outside of the present invention, with limited success. Of the quinone compounds tested in in vivo and in vitro model systems, only a small number exhibited antitumor activity (Driscoll, 1974a,b). Further, in reviewing relationships among members of biologically active natural product families and model analogs thereof, such as in the case of quinones, it was concluded that structurally simpler analogs of complex active materials typically resulted in inactive compounds (Driscoll, 1974a), thus indicating the difficulty in designing compounds for use as antitumor agents.
In the United States, cancer is the second leading cause of death. Based on current statistics, an individual born in the United States has a greater than 1 in 3 chance of developing cancer in his or her lifetime. Since the mid-1950s, it has been recognized that cancer chemotherapy can be used to cure certain cancers. Although many cancers can be cured by surgical resection, chemotherapy is often used as an adjunct to surgical therapy, and is used primarily in the treatment of nonoperable or metastatic malignancy. In view of the high number of deaths each year resulting from cancer, a continuing need exists to identify effective chemotherapeutic drugs, and particularly compounds exhibiting high antitumor activity and selectivity, for use as anticancer agents.